Scrap metal reclamation for some time has been a significant source of ferrous and nonferrous metals. Reclaimed metals can be refined to the ingot state at a cost substantially less than the cost of extracting and refining virgin metals, and these cost savings become even more significant as energy costs escalate. Scrapped automobiles are one of the most significant sources of reclaimable scrap metals, although other domestic and industrial scrap such as electric motors, printing plates, electrical cable, machinery, and home appliances also are significant sources of scrap metal.
Scrap automobiles and other scrap metal typically are initially treated by passing the scrap through a shredder, many of which are capable of reducing whole automobiles to relatively small shreds of metal and other constituent components of the original article. The nonmetallic components of the shredded articles, being significantly lighter and less dense than the metallic shreds, are relatively easily separated by flotation or other known techniques. Likewise, the ferromagnetic property of ferrous metals permits relatively economical and rapid separation of those metals from the nonferrous metallic scrap. The remaining nonferrous scrap metal, however, is not as readily separable into constituent metallic groups or alloys for further refinement and reuse. Although steel and other ferrous metals make up the bulk of most scrap metal, significant amounts of nonferrous metals and their alloys, such as aluminum, copper, lead, and zinc, are available in commercially worthwhile percentages in stocks of typical scrap metal. However, these nonferrous metals are useful only when individual constituent metals are classified and separated from each other in an effective and economical manner.
Due to the relatively low melting point of nonferrous metals such as lead and zinc, the use of thermal processes has been suggested for separating such metals from other nonferrous metals and alloys having higher melting points. Such thermal separation in a relatively crude form simply calls for subjecting the nonferrous scrap mixture to a temperature greater than the melting point of the metals to be separated. These metals, such as lead and zinc, melt and can then be mechanically separated from the remaining solids having a higher melting point. However, further refining of the lead-zinc mixture is required to classify and separate each metal.
Another prior art proposal involves selective smelting to remove lead and zinc from shredded nonferrous scrap also containing other metals. In the typical selective smelter of the prior art, at least two baths of molten liquid are provided in tandem. The first molten bath is maintained at a temperature only slightly greater than the lowest melting point of the metals to be separated in the corresponding molten baths. The temperature of the second molten bath is slightly greater than the melting point of the metal to be removed in that second bath, and so on. As the scrap metal is moved in tandem through the first bath and then the second bath, the metal having the lower melting point (e.g., lead) will melt and become separated in the first bath, and the metal having the next-higher melting point (e.g., zinc) with melt and become separated in the second bath. Additional heated baths in tandem, maintained at selected increased temperatures, can also be provided in theory, although the capital costs and energy operating costs of even a two-bath selective smelting system are substantial.
One example of apparatus for selective smelting of nonferrous metals is shown in U.S. Pat. No. 4,299,376. Another apparatus for thermal recovery of scrap metal is shown in U.S. Pat. No. 1,515,616.